UV Light Air Purifier

Some manufacturers are offering air purifiers with UV lights as an additional air cleaning stage.  They claim that their UV light air purifier “sterilises the air” and that the “air is disinfected” through the use of the UV light in their air cleaner. But is that true? Does a standalone air purifier benefit from using UV light? What does a UV light in an air purifier actually do? 

In laboratory environments, UV light - at a certain wavelength and after a certain exposure time - has been shown to kill microorganisms.  A UV light in a domestic air purifier, however, is not a reliable way to sterilize the air and is likely nothing more than just a gimmick.  Why? UV lamps in standalone air purifiers are generally too weak to do what some companies would like you to believe. If the UV light in the air purifier would be strong enough, they would create a serious health risk. The size of the air purifier and operating cost would also make it unsuitable for a domestic environment. Furthermore, there seems to be no scientific evidence that shows that UV light provides an actual benefit if used within a proper standalone HEPA air purifier.

Can a UV light air purifier sterilise the air that goes through it?

An air purifier needs to move enough air to achieve several air changes per hour in a given room to effectively clean it. If the airflow rate is high, however, contamination in the air - such as germs, microbes, fungi, and bacteria - travel through the air purifier so fast, that the exposure time of the UV light on the contamination is too short to destroy it.  

Dust and dirt can also form a ‘biofilm’ over the microorganisms, protecting it from the UV light. The bigger problem is, however, that multiple UV lamps, or even banks of UV lamps, are needed in the air purifier for the UV light exposure time to be long enough to be effective.  These banks of UV lamps would also need to be organised in a long straight configuration to maximise the exposure time.

Do you need a UV light to destroy microorganisms in the air purifier?

Some manufacturers admit that the UV light in their air purifier is not able to sterilise the air that goes through it, but argue that the UV light is needed to destroy microorganisms in the filters that collect them.  

Proper leakage-free HEPA filtration - as you find in an IQAir air purifier for example - traps and retains virtually all viruses.  A virus such as SARS-CoV-2 for example only stays viable for a couple of days, and a high-quality air purifier is designed to have a filter life of 12 months or more on average usage. Thus, there is no real benefit that a UV light in an air purifier would provide (even if it would do what some companies claim it does) if the unit uses certified and guaranteed HEPA filtration.

It is also important to point out that a UV light will never be able to shine on all parts of a proper pleated HEPA filter. Any area that is not directly exposed to the UV light - which there will be many in a pleated HEPA filter - will be unaffected by the light, making the UV lights somewhat pointless.  An additional complication is that the UV lights need to be protected from contamination (so that dust does not build upon the lamps and cover it) as well as the airflow itself, as it would cool down the UV lamps and negatively impact their effectiveness. 

Are there any health concerns regarding UV lamps in air purifiers? 

UV lamps in air purifiers do create an increased health-risk, as they can produce ozone as a by-product, as well as a disposal problem. Exposure to UV light that is strong enough to be considered of ‘germicidal wavelength’ can cause cancer and rapid sunburns. Temporary and permanent damage to the eyesight and painful inflammation of the cornea is also a risk, as exposure of such UV light to the eyesight will damage the retina. 

UV light can change in wavelength over time and produce ozone as an unwanted by-product. Ozone breaks down natural tissue, including human lung tissue. “The US Environmental Protection Agency designated 0.05 parts per million (ppm) of ozone to be a safe level. Lamps designed to release UVC and higher frequencies are doped so that any UV light below 254 nm wavelengths will not be released, to minimise ozone production. A full-spectrum lamp will release all UV wavelengths and produce ozone when UV-C hits oxygen (O2) molecules.”1

Why have a UV light in an air purifier if it is ineffective?

The likely reason why some manufacturers include UV lamps in their HEPA air purifiers is that they are more concerned with creating a compelling marketing and sales message, rather than actually creating a better air purifier.  These companies try to integrate as many different technologies into their air purifier as possible, in an effort to ‘tick all the boxes’ and knowingly or unknowingly mislead the end-customer into believing that such an air purifier will end up being superior in performance. The reality is that such a unit is likely to end up being gimmicky and relatively ineffective. 

Some of the manufacturers we have spoken with did not actually believe that they can increase the air purifier’s efficiency by including a UV light.  Nor can they guarantee that the germs will actually be killed reliably by the use of the UV lamps in their air purifier. The real reason seems to be that the UV lamps are included in the air purifiers is because the manufacturer can earn more with the replacement of UV lamps.  For safety reasons, UV lights must be changed very regularly.  As the UV lamps are cheap to manufacture or buy, and often only cost a couple of pounds, selling them to you as end customer for GBP 30.00 provides a very healthy profit margin. 

What do government organisations say about UV lights for air purification?

Many health organisations recommend that health-care institutions should not use UV light for germicidal purposes due to their unreliability and because of the false sense of security which UV lamps can create:

CDC (US Center for Disease Control and Prevention):
"The use of UV lamps and HEPA filtration in a single unit would not be expected to have any infection-control benefits not provided by use of the HEPA filter alone." (http://www.cdc.gov/mmwr/preview/mmwrhtml/00035909.htm)

"Ultraviolet (UV) lamps are not recommended in BSCs (biosafety cabinets) nor are they necessary.“ (http://www.cdc.gov/biosafety/publications/bmbl5/bmbl5_appendixa.pdf)

National Institutes of Health, Bethesda, Maryland, USA (Infection Prevention and Control Services):
„We conclude that although UVGI is microbiocidal, it is not „ready for prime time“ as a primary intervention to kill or inactivate infectious microorganisms.“ (http://www.ncbi.nlm.nih.gov/pubmed/20569852)

OSEH (Occupational Safety & Environmental Health Dept.) of Michigan University:
„The University of Michigan department of Occupational Safety and Environmental Health (OSEH) has adopted the position of the NSF, NIH, CDC and the American Biological Safety Association (ABSA) in regard to the use of UV lamps ... UV lamps are neither recommended nor required in biological safety cabinets. The use of Ultraviolet germicidal irradiation (UVGI) ... lends little to product sterility or personal safety in research settings, and has caused numerous hazardous UV exposures to employees while creating a hazardous waste disposal problem from the mercury in the bulbs. ... UV bulbs typically start to degrade and fail 6 months after installation. Without measuring the UV output there is no indication that the bulb is failing.“ (http://www.oseh.umich.edu/pdf/Uvbulb.pdf)

Ref.: 1) https://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiation